Noël Brunetière

Untangling the environmental from the dietary: dust does not matter.

Both dust and silica phytoliths have been shown to contribute to reducing tooth volume during chewing. However, the way and the extent to which they individually contribute to tooth wear in natural conditions is unknown. There is still debate as to whether dental microwear represents a dietary or an environmental signal, with far-reaching implications on evolutionary mechanisms that promote dental phenotypes, such as molar hypsodonty in ruminants, molar lengthening in suids or enamel thickening in human ancestors. By combining controlled-food trials simulating natural conditions and dental microwear textural analysis on sheep, we show that the presence of dust on food items does not overwhelm the dietary signal. Our dataset explores variations in dental microwear textures between ewes fed on dust-free and dust-laden grass or browse fodders. Browsing diets with a dust supplement simulating Harmattan windswept environments contain more silica than dust-free grazing diets. Yet browsers given a dust supplement differ from dust-free grazers. Regardless of the presence or the absence of dust, sheep with different diets yield significantly different dental microwear textures. Dust appears a less significant determinant of dental microwear signatures than the intrinsic properties of ingested foods, implying that diet plays a critical role in driving the natural selection of dental innovations.

A Deterministic Mixed Lubrication Model for Mechanical Seals

Mechanical seals are commonly used in industrial applications. The main purpose of these components is to ensure the sealing of rotating shafts. Their optimal point of operation is obtained at the boundary between the mixed and hydrodynamic lubrication regimes. However, papers focused on this particular aspect in face seals are rather scarce compared with those dealing with other popular sealing devices. The present study thus proposes a numerical flow model of mixed lubrication in mechanical face seals. It achieves this by evaluating the influence of roughness on the performance of the seal. The choice of a deterministic approach has been made, this being justified by a review of the literature. A numerical model for the generation of random rough surfaces has been used prior to the flow model in order to give an accurate description of the surface roughness. The model takes cavitation effects into account and considers Hertzian asperity contact. Results for the model, including Stribeck curves, are presented as a function of the duty parameter.

Analysis and Modeling of the Topography of Mechanical Seal Faces

The aim of this article is to provide some relevant statistical parameters for mechanical seal faces and to present some methods of modelling them in order to study mixed lubrication. Three mechanical seals with faces of three different material combinations were analyzed at three operating times (unused, run-in, and worn). Surface roughness and waviness were analyzed. Generally speaking, the amplitude of the waves tends to increase with time, whereas roughness height shows the opposite trend, except in the case of the hard faces combination. The seal surfaces are extremely skewed, this phenomenon being enhanced by wear. The surfaces are nearly isotropic with a slightly higher correlation length in the sliding direction. Two models with two different autocorrelation functions (ACFs) were used to simulate surfaces. These models, based on the Patir approach (Patir (1)), used the Johnson translation curves to impose non-Gaussian height distribution. Even if the models are able to reproduce experimental tendencies, there are some difficulties with the modeling of large structures, leading to the overestimation of summit density and underestimation of the radius of the asperities’ curvature. Generally speaking the exponential ACF gives better results than the bilinear ACF.

Seeds, browse, and tooth wear: a sheep perspective.

Abstract While grazing as a selective factor towards hypsodont dentition on mammals has gained a lot of attention, the importance of fruits and seeds as fallback resources for many browsing ungulates has caught much less attention. Controlled‐food experiments, by reducing the dietary range, allow for a direct quantification of the effect of each type of items separately on enamel abrasion. We present the results of a dental microwear texture analysis on 40 ewes clustered into four different controlled diets: clover alone, and then three diets composed of clover together with either barley, corn, or chestnuts. Among the seed‐eating groups, only the barley one shows higher complexity than the seed‐free group. Canonical discriminant analysis is successful at correctly classifying the majority of clover‐ and seed‐fed ewes. Although this study focuses on diets which all fall within a single dietary category (browse), the groups show variations in dental microwear textures in relation with the presence and the type of seeds. More than a matter of seed size and hardness, a high amount of kernels ingested per day is found to be correlated with high complexity on enamel molar facets. This highlights the high variability of the physical properties of the foods falling under the browsing umbrella.

A Simple and Easy-To-Use TEHD Model for Non-Contacting Liquid Face Seals

Numerous studies have shown that the properties of non-contacting liquid face seals depend greatly on thermal effects. A complex numerical TEHD (ThermoElastoHydroDynamic) model is needed to accurately determine seal temperature. Moreover, this temperature is influenced by a significant number of parameters (such as operating conditions or seal ring shape). This makes the task of design and optimization of mechanical face seals difficult. This paper presents a simple and easy-to-rise TEHD model, which allows for the determination of mean face temperature, power loss, leakage rate, axial stiffness and fluid film thickness. It is demonstrated that the results depend on a single dimensionless parameter. The simplified model is validated by comparison with an accurate numerical TEHD model.

A Multiscale Approach to the Mixed Lubrication Regime: Application to Mechanical Seals

This paper presents a multiscale approach to solve the problem of mixed lubrication in mechanical seals. In fact, the lubricating fluid film developed between the faces of mechanical seals is usually a fraction of a micron in thickness, leading to a mixed lubrication regime. However, over a velocity threshold the fluid film can completely separate the faces because of the hydrodynamic effect due to the surface roughness, even if the surfaces are nominally parallel. To study this phenomenon, a deterministic model is preferable because the stochastic theory based on flow factors is unable to reproduce this effect. Unfortunately, a deterministic approach needs a prohibitive amount of nodes and computation time. This is why a multiscale model is proposed. It is composed of a micro-deterministic model working on a small area coupled with a macro model giving the pressure distribution on a macro-mesh. The results of the multiscale model are compared to those of a pure deterministic model in terms of accuracy and computation time when the area of the macro-cells is varied.

Thermoelastohydrodynamic Behavior of Mechanical Gas Face Seals Operating at High Pressure

A numerical modeling of thermoelastohydrodynamic mechanical face seal behavior is presented. The model is an axisymmetric one and it is confined to high pressure compressible flow. It takes into account the behavior of a real gas and includes thermal and inertia effects, as well as a choked flow condition. In addition, heat transfer between the fluid film and the seal faces is computed, as are the elastic and thermal distortions of the rings. In the first part of this paper, the influence of the coning angle on mechanical face seal characteristics is studied. In the second part, the influence of the solid distortions is analyzed. It is shown that face distortions strongly modify both the gap geometry and the mechanical face seals performance. The mechanical distortions lead to a converging gap, while the gas expansion, by cooling the fluid, creates a diverging gap.

The Effect of Inertia on Radial Flows—Application to Hydrostatic Seals

A theoretical study of thin fluid film flows between rotating and stationary disks is presented. Inertia terms are included using an averaged method. It is assumed that inertia effects do not influence the shape of velocity profiles. It is shown that this assumption applies in many cases encountered in fluid film lubrication. The model is validated by comparison with experimental data and previous theoretical studies. A thermoelastohydrodynamic analysis of a hydrostatic seal is performed. The substantial influence of inertia terms on leakage rate prediction is demonstrated.

A Simple Approach to the ThermoElastoHydroDynamic Behavior of Mechanical Face Seals

This article presents a semi-analytical analysis of non-contacting mechanical face seals. The model takes account of thermal effects and face distortions that generally determine the performance of mechanical seals. It is shown that the seal behavior is a function of just two dimensionless parameters: (a) the sealing number Se, which depends on the operating and design parameters of the seal, and (b) the coning number Co, which is the ratio of elastic and thermal distortions. The theoretical results are compared to measurements obtained on an inner pressurized seal. Good agreement on the temperature of the faces and on dissipated power is obtained for various rotation speeds, validating the assumptions used in developing the model. The analysis of the influence of Se and Co on the behavior of mechanical face seals makes it possible to highlight several operating modes.

Three-dimensional dental microwear texture analysis and diet in extant Suidae (Mammalia: Cetartiodactyla)

Abstract We investigated the dietary differences among four extant suid genera using 3D dental microwear texture analysis on the enamel surfaces of molar shearing facets. We tested the differences among four taxa for four variables: complexity, anisotropy, and heterogeneity at two scales. This enabled us to distinguish omnivorous taxa (Sus scrofa and Potamochoerus sp.) from herbivorous ones (Phacochoerus africanus and Hylochoerus meinertzhageni) in terms of complexity. Heterogeneity likely distinguishes the suids displaying specialized diets (homogenous surfaces in the grazer Ph. africanus) from the more generalized suids (heterogeneous surfaces in the omnivorous S. scrofa and Potamochoerus sp., and mixed feeder herbivorous H. meinertzhageni). This study represents the first step toward a better comprehension of the diet and ecology of extant and fossil suids and also puts forward new hypotheses to be tested, especially on the effects of rootling behavior.